Traditionally, millimeter-wave (MMW), sub-millimeter-wave (sub-MMW), and Terahertz radios are implemented with multiple chips fabricated in III-V semiconductor technologies. As devices used can generate larger output power, the requirement for the transmission loss from the radio frequency (RF) output to the antenna input is relaxed. When a radio having a transmitter (Tx) and receiver (Rx) uses multi-chip module technology, the MMW antenna may be connected to the Tx or Rx RF output by a combination of bonding wires and wire lines, or by a combination of flip chip connection and wire line. The wire line is necessary because the multi-chip module solution of the Tx or Rx does not allow for the Tx or Rx module to approach the antenna closely.
Driven by demand for low cost and small-sized MMW radio, the system-on-chip (SoC) or system-in-package (SiP) solutions of MMW radios have been proposed. An example of a SoC MMW radio in Silicon-Germanium (SiGe) or complementary metal oxide semiconductor (CMOS) involves a MMW antenna being fabricated on the substrate. The antenna is then connected to the Tx or Rx chip by bonding wires. Another example involves a MMW antenna sitting on an antenna socket. The socket may be made of a low-loss dielectric material or a hollow metal filled with foam or air. The antenna is then connected to Tx or Rx chip by flip chip technology.
The feeding from RF output to the antenna usually involves contact coupling or in particular inductive feeding due to inherent stray inductances in wire lines, bond wires and flip chip connection for example. MMW AiP designs using this inductive feeding may meet great challenges in impedance matching and reduction of transmission loss. This is because the reactance due to (stray) inductance increases proportionately with frequency. It may be difficult to achieve wide impedance matching bandwidth using this inductive feeding. For example, the bond wire feeding at 60 GHz is extremely difficult to be realized in MMW AiP designs.
Several attempts have been made to address these problems due to the stray inductance so as to enable realization of MMW AiP design. One possible approach to solve this problem may involve contactless coupling or alternating current coupling. Contactless coupling may involve capacitive coupling or inductive coupling for example.
One such attempt involves a microstrip antenna array having a broadband linear polarization, and circular polarization with high polarization purity. The feedlines of the array are capacitively coupled to feeding patches at a single feedpoint or at multiple feedpoints, the feeding patches in turn being electromagnetically coupled to corresponding radiating patches.
Another such attempt involves a microstrip antenna in low temperature co-fired ceramic (LTCC). The antenna is excited by proximity-coupling or capacitive coupling and has a total thickness of 12 metal layers and 11 substrate layers. The use of proximity-coupling allows for different polarization reception of signals that exhibits improved cross-channel isolation in comparison to a traditional coplanar microstrip feed. There are two substrate layers separating the patch and the feedline, and two substrate layers separating the feedline and the ground layer. The remaining seven substrate layers are used for burying RF circuitry beneath the antenna that includes the filter, integrated passives, and other components.
However, there is still a need for an alternative antenna-in-package design which advantageously avoids or reduces some of the above-mentioned drawbacks of prior art devices.